With the increasing density of devices on a semiconductor chip and ever more complex applications there is a need to form ever smaller and more precise electrical connections when packaging such semiconductor chips, especially medium and higher end products with high input/output counts.
In one conventional method, electrical connections in packaged electronic components are made using electrical contacts in the form of solder bumps which are deposited by a solder deposition process on contact pads of one of two components to be interconnected, the solder deposition process requiring special alignment techniques, such as the application of a masking resist to the surface of the component to define the individual locations at which solder bumps are to be deposited. The masking layer then has to be subsequently removed after the solder has been deposited on the surface.
In another known method, solder paste is screen printed on the contact pads of a component using a metal mask. The use of such metal masks means that accurate alignment techniques are required to deposit the paste on individual pads and that the chance of bridging between pads increases as the pitch decreases.
In yet another known process for making electrical connections, a contact on one component is connected to a metal stud on another components using an electrically conducting adhesive material which contains metal particles. Because only a few of the metal particles in the adhesive material make an electrical connection with the stud, the electrical resistance of such an connection is rather high.
With the ever smaller size, higher packing density and complexity of semiconductor devices in semiconductor chips, the electronic component packaging industry is increasingly being faced with the need to provide more closely packed electrical connections of smaller and smaller area whilst maintaining the electrical isolation and integrity of the individual connections.
Because the required dimensions of solder joints are therefore steadily shrinking and solders have an intrinsically low melting point, the electrical resistance, the mechanical strength and the susceptibility of such joints to electro-migration are becoming increasingly important factors.
It is becoming increasingly troublesome to form satisfactory connections of the required small size and at the required small pitch using these known connection-forming techniques. For example, it is extremely difficult and relatively expensive to form solder bumps by conventional methods with a bump size of 75 μm or less at a pitch of 125 μm or less.